1. Field of the Invention
The present invention relates to a novel under-frame structure which is applicable with advantage to a coupler of a low-floor articulated car, typically a streetcar.
2. Description of the Related Art
FIG. 9 is a schematic plan view for explaining the principle of the under-frame structure of the conventional articular joint. The conventional under-frame comprises a bearing outer ring 51 secured rigidly to a first particular member projecting from a first car C1 toward a second car C2 and a bearing inner ring 52 having a pair of mounting segments 53, 53 adapted to hold a coupling shaft 54, a second articular member 55 projecting from the second car C2 toward the first car C1 to grip said coupling shaft 54, whereby the first and second cars C1, C2 are coupled through a bearing 50.
However, since this conventional under-frame is of a construction such that the bearing 50 and the coupling shaft mounting segments 53, 53 are simply stacked up, a considerable difference in level is inevitable between the first articular member and the second articular member, with the result that the surface level of the floor on which passengers set their feet cannot be sufficiently lowered.
However, particularly in the case of a streetcar, the floor level is preferably as low as possible from the consideration of the ease of boading and unboading by elderly or physically handicapped passengers.
In view of the above demand, the present invention has for its object to provide an under-frame structure which does not present a strength problem or interfere with coupler performance and, yet, makes it possible to lower the level of the floor on which passengers set their feet.